How to get rid of fireflies in my metallic materials / cycles (principled bsdf)
First try to set Strength in your Normal Map to something less. For example 0,02. If that won't do much, set Clamp Direct to 8 and Clamp Indirect to 6 in Sampling settings (image below). If that won't help either, or difference still won't be good enough, add to each metallic material on your scene Mix Shader in which mix your current setup with Transparent BSDF by Factor of Is Reflection Ray from Light Path node (also image below). Good luck.